My current character is a Black Dragonborn 6th level shadow sorcerer and lvl 1 fighter. He has medium armor feat. His stats are 8 str, 16 dex, 12 con, 11 Intel, 12 Wis, 19 Cha,  and 21 AC. His backstory is that he is a spy for the Shadow Thieves dealing mostly in information and not so much thieving, he was branded an ill omen due to his shadow powers and was abandoned by his Clan. His motivation is to find out what Clan he belonged to and then destroy them for abandoning him in a cave to the under dark as a child as a sacrificial offering. I was debating pushing Fighter to level 4 but what subclass to pair with his spell casting. He has a mix of melee and ranged spells and I plan to use the Eyes of the Dark on him as well for extra flair and given most of the enemies will have disadvantage trying to attack him and he would have advantage being able to see in the magical darkness if casted with Sorcery Points, but he will be weaponless as his free hand will be holding his arcane focus and the other a shield. Rune Knight was the sub class I was looking into the most for Cloud Rune and most likely Stone Rune. I do have the ability to completely scrap fighter after level 1 and maybe going Bard College of Whispers would also fit in well with my shadow sorcery / spy, as well as Rogue I could drop my shield and still have a base of 19 AC and be a little more of a skill monkey but again not sure what subclass to push maybe Mastermind or Inquisitive. 

Any reason for not continuing with Sorcerer? Spells and sorcery points aside, sticking with fewer classes is your fastest route to a higher proficiency bonus and to your next ASI. If you're doing it for roleplay reasons that's totally fine, but then I'd expect you to have a better idea of what you'd want already. If you'd be going for something cheesy like a SorLock that'd be fine too, but the options you lay out aren't optimized like that. I guess I can't really tell what you're looking for, and that makes it hard to suggest anything.

I'm trying to plot what I should do for my next step. not against just going full sorcery with this build as well. Just was thinking more way to add to the idea of being a spy but I can focus on illusion magic as well so that would work. I'm basically overthinking myself

I'd actually recommend Echo Knight over Rune Knight if your intent is to be more of a sneaky, spy-like character... there's nothing particularly sneaky about growing to Large size. Echo Knight pairs well with our mix of range and Melee skills, since you can use your Echo to bamf all over the battlefield and you can stay physically 30 feet away from a target to hit it with ranged spells and abilities from yourself, while simultaneously having your Echo next to that same enemy using Melee attacks as you see fit. 

The other important thing is that your echo gives you some cool spy moves as well. The obvious feature is that you can use it to quickly teleport in or out of any place where you get clear line of sight. If a building has an open window or even a crack big enough for you to see through, you can get inside. Once you hit higher levels you can also see through your Echo and use it as a scout to check things out for you without putting yourself in any danger. It's honestly kind of broken, since it has so many cool abilities with zero cost that you can just do over and over again.

It's fine. Really, anything can be fine. You just have to like it. But if you're asking for advice, it helps if we have an idea of what it is you'd like. :p

yeah It's one of my biggest issues is always getting way to ahead of myself in plotting my character out. I would really like him to be a stealth character and he already is with his dex and having criminal / spy background, someone who can move in and out of shadows, infiltrate and extract information. I want him to be able to read people and the battlefield well and then make the ability to chose how to proceed. I figured with the ability to use sorcery points and cast darkness on myself and see through it would be an extremely cool ability to couple with sneak attack as well as get lots of skill monkey abilities. That was the main reason I was leaning to going Inquisitor or Mastermind coupled with Sorcery but I would have to focus the bulk of my levels going forward on that and basically limit my spell casting ability and that's probably not the best option. Where I can pick up skills through feats and just keep leveling my sorcery and build my spell casting ability.

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I'd actually recommend Echo Knight over Rune Knight if your intent is to be more of a sneaky, spy-like character... there's nothing particularly sneaky about growing to Large size. Echo Knight pairs well with our mix of range and Melee skills, since you can use your Echo to bamf all over the battlefield and you can stay physically 30 feet away from a target to hit it with ranged spells and abilities from yourself, while simultaneously having your Echo next to that same enemy using Melee attacks as you see fit. 

The other important thing is that your echo gives you some cool spy moves as well. The obvious feature is that you can use it to quickly teleport in or out of any place where you get clear line of sight. If a building has an open window or even a crack big enough for you to see through, you can get inside. Once you hit higher levels you can also see through your Echo and use it as a scout to check things out for you without putting yourself in any danger. It's honestly kind of broken, since it has so many cool abilities with zero cost that you can just do over and over again.

Unfortunately Echo Knight isn't an available option for me with the source books we are using. But this sounds cool as hell.

That's too bad that you can't use Echo Knight, but in that case I think I would recommend instead  Battlemaster. It's crazy versatile and it lets you build a fighter custom-built for whatever style of combat you prefer. Using your Shadow Sorcerer ability to create darkness around yourself, I'd recommend the Riposte and Tripping Attack maneuvers. Tripping Attack seems a bit redundant, because you can already get advantage on an enemy just from the darkness, but the more important feature is that knocking them prone makes it much harder for them to escape your darkness, since any opponent will have to use half their movement just to get up, so they either need to Dash to get out and eat an opportunity attack, or disengage and if they're not still in the darkness by the end of their turn they'll still be right on the edge of it. They might just choose to stay in the darkness and fight you outright, and since they have disadvantage on attacks they'll likely miss you and trigger Riposte to punish them for it. Grab the Sentinel feat as soon as possible and you can basically just pick one opponent in combat and pin them down all on your own, just be ready to drop the darkness after a bit so your allies can see what they're doing.

Another option, if you want to lean more into the social aspect of being a spy, is actually the Samurai subclass. It lets you take proficiency in Insight or Persuasion... it even eventually lets you add your WIS modifier to Persuasion rolls, and gives you proficiency in WIS saving throws. Depending on your WIS score that might not be particularly tempting, but it does lend itself more to social infiltration, and the ability to just straight up give yourself Advantage for a full turn isn't bad, although you've got a bit of a wait before getting access to Extra Attack to really make it worth the investment.